Gas spring assembly for a vehicle suspension system

ABSTRACT

A vehicle includes a body, a pair of front gas springs coupling a pair of front wheel end assemblies to the body, and a pair of rear gas springs coupling a pair of rear wheel end assemblies to the body. At least one of the rear gas springs includes a cylinder, a rod extending within the cylinder and movable relative to the cylinder, the rod and the cylinder together at least partially defining a chamber having a variable volume and receiving a first pressurized gas therein, and an accumulator in communication with the chamber and containing a second pressurized gas therein. The second pressurized gas within the accumulator is held at a threshold pressure creating a first spring rate when the first pressurized gas is below the threshold pressure and a second spring rate when the first pressurized gas is above the threshold pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/515,631,filed Jul. 18, 2019, which is a continuation of application Ser. No.15/631,800, filed Jun. 23, 2017, now U.S. Pat. No. 10,421,332, which isa continuation of application Ser. No. 14/671,650, filed Mar. 27, 2015,now U.S. Pat. No. 9,688,112, which is a continuation of application Ser.No. 14/305,812, filed Jun. 16, 2014, now U.S. Pat. No. 8,991,834, whichis a continuation of application Ser. No. 13/908,785, filed Jun. 3,2013, now U.S. Pat. No. 8,764,029, which is a continuation ofapplication Ser. No. 12/872,782, filed Aug. 31, 2010, now U.S. Pat. No.8,465,025, all of which are incorporated herein by reference in theirentireties.

BACKGROUND

The present application relates to suspension systems for vehicles. Morespecifically, the present application relates to a gas spring for asuspension system.

SUMMARY

One embodiment relates to a vehicle including a body, a pair of frontwheel end assemblies, a pair of front gas springs coupling the frontwheel end assemblies to the body, a pair of rear wheel end assembliespositioned rearward of the front wheel end assemblies, and a pair ofrear gas springs coupling the rear wheel end assemblies to the body. Atleast one of the rear gas springs includes a cylinder, a rod extendingwithin the cylinder and movable relative to the cylinder, the rod andthe cylinder together at least partially defining a chamber having avariable volume and receiving a first pressurized gas therein, and anaccumulator in communication with the chamber and containing a secondpressurized gas therein. The second pressurized gas within theaccumulator is held at a threshold pressure creating a first spring rateopposing relative movement between the rod and the cylinder when thefirst pressurized gas within the chamber is pressurized below thethreshold pressure and a second spring rate opposing relative movementbetween the rod and the cylinder when the first pressurized gas withinthe chamber is pressurized above the threshold pressure.

Another embodiment relates to a vehicle including a vehicle body and avehicle suspension system supporting the vehicle body. The vehiclesuspension system has a gas spring. The gas spring includes a cylinderdefining an inner chamber, a rod disposed within the cylinder andmovable relative to the cylinder to adjust a volume of the innerchamber, and a sensor attached to at least one of the rod and thecylinder. The sensor is configured to provide a signal indicative of aride height of the vehicle suspension system based upon a relativeposition of the rod and the cylinder.

Yet another embodiment relates to a vehicle including a body, a pair offront wheel end assemblies, a pair of front gas springs coupling thefront wheel end assemblies to the body, a pair of rear wheel endassemblies positioned rearward of the front wheel end assemblies, and apair of rear gas springs coupling the rear wheel end assemblies to thebody. At least one of the rear gas springs includes a rod movablerelative to a cylinder, the rod and the cylinder collectively defining avariable volume chamber therebetween, and an accumulator in gaseouscommunication with the variable volume chamber. The variable volumechamber receives a first gas and the accumulator receives a second gasfluidly separate from the first gas, the second gas being pressurized toa threshold pressure. The first gas provides different spring rates whenthe first gas is above or below the threshold pressure.

Alternative exemplary embodiments relate to other features andcombinations of features as may be generally recited in the claims.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, in which:

FIG. 1 is a perspective view of an axle assembly, according to anexemplary embodiment of the invention.

FIG. 2 is a perspective view of a suspension system, according to anexemplary embodiment of the invention.

FIG. 3 is a perspective view of a gas spring in a first configuration,according to an exemplary embodiment.

FIG. 4 is a side view of the gas spring of FIG. 3 in a secondconfiguration.

FIG. 5 is a side view of a gas spring assembly, according to anexemplary embodiment of the invention.

FIG. 6 is a front view of the gas spring assembly of FIG. 5.

FIG. 7 is a sectional view of the gas spring assembly of FIG. 6, takenalong line 7-7 of FIG. 7.

FIG. 8 is a detail view of a portion of the gas spring assembly of FIG.7, taken along line 8-8 of FIG. 7.

FIG. 9 is a detail view of a portion of the gas spring assembly of FIG.7, taken along line 9-9 of FIG. 7.

FIG. 10 is a graphical comparison of force versus displacement for asingle-stage gas spring and a two-stage gas spring based upon simulationdata, according to an exemplary embodiment of the invention.

FIG. 11 is a schematic diagram of an accumulator, according to anexemplary embodiment of the invention.

FIG. 12 is a schematic diagram of an accumulator, according to anotherexemplary embodiment of the invention.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplaryembodiments in detail, it should be understood that the presentapplication is not limited to the details or methodology set forth inthe description or illustrated in the figures. It should also beunderstood that the terminology is for the purpose of description onlyand should not be regarded as limiting.

According to an embodiment, a vehicle may include a body supported by asuspension system (see, e.g., suspension system 218 as shown in FIG. 1).In some embodiments, the vehicle may be a military vehicle. In otherembodiments, the vehicle may be a utility vehicle, such as a fire truck,a tractor, construction equipment, or a sport utility vehicle. Thevehicle may be configured for operation on both paved and rough,off-road terrain. As such, the suspension system may be correspondinglyconfigured to support the weight of the vehicle while providingcomfortable ride quality on both paved and rough, off-road terrain. Insome embodiments, the suspension system is configured to change the rideheight of the vehicle by lifting or lowering the body of the vehiclewith respect to the ground.

Referring to FIG. 1, an axle assembly 210 is configured for use with thevehicle. According to an exemplary embodiment, the axle assembly 210includes a differential 212 connected to half shafts 214, which are eachconnected to a wheel end assembly 216. The wheel end assembly 216 is atleast partially controlled (e.g., supported) by a suspension system 218,which includes a spring 220, a damper 222, an upper support arm 224, anda lower support arm 226 coupling the wheel end assembly 216 to thevehicle body or part thereof (e.g., chassis, side plate, hull).

According to an exemplary embodiment, the differential 212 is configuredto be connected with a drive shaft of the vehicle, receiving rotationalenergy from a prime mover of the vehicle, such as a diesel engine. Thedifferential 212 allocates torque provided by the prime mover betweenhalf shafts 214 of the axle assembly 210. The half shafts 214 deliverthe rotational energy to the wheel-end assemblies 216 of the axleassembly 210. The wheel end assemblies 216 may include brakes, gearreductions, steering components, wheel hubs, wheels, and other features.As the vehicle travels over uneven terrain, the upper and lower supportarms 224, 226 at least partially guide the movement of each wheel endassembly 216, and a stopper 228 provides an upper bound to movement ofthe wheel end assembly 216.

Referring to FIG. 2, according to an exemplary embodiment the suspensionsystem 218 includes one or more high-pressure gas components, where thespring 220 is a high-pressure gas spring 220. In some embodiments, thesuspension system further includes at least one high-pressure gas pump230. In some such embodiments, the suspension system 218 includesseparate high-pressure gas pumps 230 associated with each spring 220 anddamper 222 set. In preferred embodiments, the gas of the pump 230,spring 220, and damper 222 includes (e.g., is at least 90%, at least95%) an inert gas such as nitrogen, argon, helium, etc., which may bestored, provided, or received in one or more reservoirs (e.g., centralreservoir, tank) (not shown).

During operation, the pump 230 selectively provides gas, under pressure,to the high-pressure gas spring 220 and/or to reservoirs, tanks,accumulators, or other devices. In some contemplated embodiments, two ormore high-pressure gas dampers 222 of the vehicle are cross-plumbed vialines 232 (e.g., hydraulic lines) connecting dampers 222 on oppositesides of the axle assembly 210, between dampers 222 in a “walking beam”configuration for a tandem axle, or between dampers 222 on separate axleassemblies of the vehicle (e.g., between dampers located front-to-back,or diagonally located with respect to each other).

Referring to FIGS. 3-4, a gas spring 310 includes a cylinder 312 coupledto a rod 314 (FIG. 4). The cylinder 312 has a cap end 316, a rod end318, and a side wall 320 (e.g., cylindrical side wall) extending betweenthe cap and rod ends 316, 318. A chamber (see, e.g., chamber 418 asshown in FIG. 7) is formed between the cylinder 312 and the rod 314—suchas interior to the cylinder 312, between the cap end 316, the side wall320, and the rod 314, which extends through the rod end 318 of thecylinder 312. Nitrogen or another gas held in the chamber compresses orexpands in response to relative movement between the rod 314 and thecylinder 312 to provide the receipt, storage, or release of potentialenergy by the gas spring 310.

The rod 314 is configured to translate with respect to the cylinder 312.According to an exemplary embodiment, the rod 314 is coupled to orcomprises a piston (see, e.g., rod 414 as shown in FIG. 7; e.g., rodend, plunger) that forms a wall of the chamber. When the rod 314translates relative to the cylinder 312, the piston changes the volumeof the chamber, compressing the gas in the chamber or allowing the gasto expand. The gas in the chamber resists compression, providing a forcethat is a function of the compressibility of the gas, the area of thepiston, the volume and geometry of the chamber, and the current state(e.g., initial pressure) of the gas, among other factors. As such, thegas spring 310 receives potential energy, stored in the gas, as the gasis compressed and releases the potential energy as the gas expands.

The cylinder 312 of the gas spring 310 is preferably cylindrical due tostructural benefits associated with cylindrical pressure vessels.However, in other contemplated embodiments, the cylinder 312 may besubstituted for a body having another geometry. In some contemplatedembodiments, the chamber may be formed in, or at least partially formedin the rod 314. In one such embodiment, the chamber spans both thecylinder 312 and at least a portion of the interior of the rod 314.

In some embodiments, the gas spring 310 includes at least one port 322(e.g., aperture, inlet) that may be opened to allow gas (e.g., inertgas) to be provided to or from the chamber. The chamber of the gasspring is substantially sealed when the port 322 is not open. In someembodiments, the port 322 may be coupled to an accumulator (see, e.g.,accumulator 416 as shown in FIG. 5), to a pump (see, e.g., pump 230 asshown in FIG. 2), or to one or more reservoirs (not shown). In someembodiments, the gas spring 310 includes separate ports associated withthe accumulator and the pump.

In some embodiments, the gas spring 310 further includes at least oneport 324 that may be opened to allow a pressurized reservoir of a higheror a lower pressure (see generally accumulator 416 as shown in FIG. 5)to be coupled to the gas spring 310. Coupling the higher pressurereservoir to the gas spring 310 increases the pressure in the gas spring310, causing the gas spring 310 to expand and increasing the ride heightof the axle assembly. Conversely, coupling the lower pressure reservoirto the gas spring 310 decreases the pressure in the gas spring 310,causing the gas spring 310 to contract and decreasing the ride height ofthe axle assembly. In some embodiments, the gas spring 310 includesseparate ports 324 for providing hydraulic fluid to the internal volumeand for receiving hydraulic fluid from the internal volume.

In other contemplated embodiments, the gas spring 310 is coupleddirectly to a pump (see, e.g., pump 230 as shown in FIG. 2), to increaseor decrease pressure in the gas spring 310 corresponding to a desiredride height. In still another contemplated embodiment, a gas springfurther includes at least one port that may be opened to allow hydraulicfluid (e.g., oil) to be provided to or from an internal volume (see,e.g., internal volume 432 as shown in FIG. 8) of the gas spring. Theinternal volume for hydraulic fluid is separated from the chamber forgas. In such contemplated embodiments, adding or removing of hydraulicfluid from the internal volume changes the overall length of the gasspring for different ride heights of the suspension system. Howeverusing pressurized gas to change the length of the gas spring 310 may bepreferable in some embodiments because of reduced losses (e.g.,friction, drag) associated with a flow of gas (e.g., nitrogen) comparedto hydraulic fluid (e.g., oil).

Referring now to FIGS. 5-9, a gas spring assembly 410 includes acylinder 412 coupled to a rod 414, and an accumulator 416. A firstchamber 418 (FIG. 7) is formed between the cylinder 412 and the rod 414and a second chamber 420 is formed in the accumulator 416. According toan exemplary embodiment, the accumulator 416 includes a rigid exterior424 (e.g., shell, housing) and a flexible, inflatable bladder 426 withinthe rigid exterior 424. The second chamber 420 is located between therigid exterior 424 and the bladder 426. According to an exemplaryembodiment, the accumulator 416 is positioned proximate to the cylinder412 and rod 414, and the second chamber 420 of the accumulator 416 isconnected to the first chamber 418, formed between the cylinder 412 androd 414, by way of a gas transfer conduit 422. The gas transfer conduit422 may include a valve 428 (e.g., check valve, poppet) for controllingaccess between the first and second chambers 418, 420. The valve 428 mayserve to optionally disconnect the accumulator 416 from the firstchamber 418, or to optionally contain gas in the second chamber 420having a pressure exceeding or lower than gas in the first chamber 418.

In some embodiments, when the valve 428 is open, the first chamber 418is in gaseous communication with the second chamber 420 such that acontinuous body of gas extends between the two chambers 418, 420. Nointermediate hydraulic fluid or mechanical element is included totransfer energy from the first chamber 418 to the second chamber 420 orvice versa. In some such embodiments, the only hydraulic fluidassociated with the gas spring assembly 410 is a thin film between therod and cylinder that moves during compression or extension of the rod414. Use of the continuous body of gas for gaseous communication betweenthe first and second chambers 418, 420 is intended to reduce frictionallosses associated with energy transfer between the first and secondchambers 418, 420, as may otherwise occur with hydraulic or mechanicalintermediate elements. However, in other contemplated embodiments,hydraulic or mechanical intermediate elements may be used.

During use of the gas spring assembly 410, in some embodiments, thebladder 426 is inflated to an initial pressure. As the rod 414 andcylinder 412 are moved together, such as when the associated vehicledrives over a bump, gas in the chamber 418 compresses, providing a firstspring rate for the gas spring assembly 410. In such embodiments, thepressure of the gas in the first chamber 418 is communicated to theaccumulator 416 via the gas transfer conduit 422. If the pressure of thegas communicated from the first chamber 418 is below the initialpressure of the bladder 426, the gas spring assembly 410 will respond tothe bump with the first spring rate. However, if the pressure of the gascommunicated from the first chamber 418 exceeds the initial pressure inthe bladder 426, then the bladder 426 will compress, increasing theeffective volume of the second chamber 418, which provides a secondspring rate to the gas spring assembly 410.

In some such embodiments, a pump (see, e.g., pump 230 as shown in FIG.2) may be coupled to the bladder 426 to increase the initial pressure ofthe bladder 426 and thereby increase the threshold amount of loadingrequired to achieve compression of the bladder 426, which would increasethe loading required to initiate the second spring rate. Or gas may bereleased from the bladder 426 to decrease the threshold. As such, thevalue of the initial pressure of the bladder 426 may be set to achieve adesired responsiveness of the gas spring assembly 410. Use of the firstand second spring rates is intended to reduce peak forces on thevehicle, improving the ride quality and durability of the vehicle.Tuning of the threshold allows for adjustment of the response of the gasspring assembly 410 depending upon a particular vehicle application.

FIG. 10 includes a graphical representation 510 of spring force 512 as afunction of spring deflection 514 for a single-stage spring 516 (withoutaccumulator) and two-stage spring 518 (with accumulator) based uponsimulation data (i.e., prophetic representation). As spring deflection514 increases, the spring force 512 of the spring correspondinglyincreases. For lesser loads, the relationship between spring deflection514 and spring force 512 is substantially direct (e.g., quadratic, buthaving a substantially straight slope). However, when loading of thespring reaches a threshold 520, the spring rate (i.e., slope of thecurve) of the two-stage spring 518 decreases, while the spring rate ofthe single-stage spring 516 continues along the same trajectory (e.g.,quadratic curve). The point of inflection 522 along the two-stage spring518 curve is adjustable by increasing or decreasing the initial pressurein the bladder.

Referring again to FIGS. 5-9, according to an exemplary embodiment, thegas spring assembly 410 includes at least one port 430 (FIG. 8) to allowhydraulic fluid to be provided to an internal volume 432 within the gasspring assembly 410. Hydraulic fluid passes through the port 430 andalong a conduit 434, which distributes the hydraulic fluid into theinternal volume 432 by way of a distribution element 436 (e.g.,perforated plate).

In some embodiments, a floating, annular piston 438 is used to separatethe hydraulic fluid in the internal volume 432 from the gas of thechamber 418. Standard or conventional hydraulic seals 440 may be usedwith respect to the annular piston 438 and port 430 of the internalvolume 432 to prevent leakage of the hydraulic fluid. In someembodiments, standard accumulator seals are used to seal the annularpiston 438. According to an exemplary embodiment, the internal volume432 surrounds at least a portion of the first chamber 418 (for gas)within the gas spring assembly 410. As such, the hydraulic seals 440serve to seal the gas within the gas spring assembly 410.

According to an exemplary embodiment, the gas spring assembly furtherincludes a sensor 442 integrated with the gas spring assembly 410 andconfigured to sense the relative configuration of the rod 414 andcylinder 412. In some embodiments, the sensor 442 provides a signal(e.g., digital output) that is indicative of the ride height of theassociated suspension system (see, e.g., suspension system 218 as shownin FIG. 1) based upon the relative configuration of the rod 414 andcylinder 412. In contemplated embodiments, the sensor 442 includes alinear variable differential transformer (LVDT), where a shaft of theLVDT extends through the cylinder 412 to the rod 414. As the rod 414 andcylinder 412 move relative to one another, the shaft of the LVDTprovides a signal (e.g., inductive current) that is a function of themovement of the shaft.

Referring now to FIG. 11, an accumulator 610 includes a cylinder 612having a first section 614 and a second section 616. In someembodiments, the first section 614 has a narrower cross section than thesecond section 616. The accumulator 610 further includes a pistonassembly 618 having a first face 620 corresponding to the first section614 and a second face 622 corresponding to the second section 616. Aninlet 624 is coupled to the first section 614 and is configured to be ingaseous communication with gas from a chamber of a gas spring (see,e.g., chamber 418 as shown in FIG. 7). As gas is provided to the firstsection 614, the piston assembly 618 is moved, compressing a separatebody of gas 626 in the second section 616. Compression of the secondbody of gas 626 receives potential energy, stored in the compressed gas.

In some embodiments, the accumulator 610 additionally includes atransfer tube 628 extending between the first and second sections 614,616. The transfer tube 628 allows for controlled transfer of gas fromthe second section 616 to the first section 614, or vice versa. Arestrictor 630 or valve may be positioned along the transfer tube 628 tocontrol the flow of gas through the transfer tube 628. FIG. 12 shows analternate embodiment of an accumulator 710 where a transfer tube 712 andrestrictor 714 or valve is integrated with a piston assembly 716.

In some embodiments that include the transfer tube 628, 712, the twosections 614, 616 of the accumulator 610 are in gaseous communication atequilibrium (e.g., steady state). Equal pressure acts on both sides ofthe piston assembly 618, 716. But, due to the unequal cross-sections, anet force biases the piston assembly 618, 716 toward the first section614. At standard operating pressures of the gas spring, the equilibriumpressure supplies a net force sufficient to overcome forces of gravityand friction acting on the piston assembly 618, 716.

During an impulse loading event, the spring compresses and rapidlycommunicates increased gas pressure to the first section 614 of theaccumulator 610. However, due in part to the setting of the restrictor630 and drag in the transfer tube 628, 712, the pressure in the secondsection 616 of the accumulator 610 does not increase as rapidly. Assuch, with a sufficient pressure differential between the first andsecond sections 614, 616, the piston assembly 618, 716 moves from theinitial position. The volume of the first section 614 increases and thevolume of the second section 616 decreases, compressing the gas in thesecond section 616, which results in a different spring rate (see, e.g.,point of inflection 522 as shown in FIG. 10) for the overall gas springassembly.

According to an exemplary embodiment, the second spring rate andthreshold at which the bias of the piston assembly 618, 716 is overcomeis tunable by changing the area ratio of the piston assembly 618, 716(i.e. chamber cross-sections). In some contemplated embodiments, thesetting of the restrictor 630 controls damping to the accumulator 610and overall gas spring assembly, which may be used with or without aseparate damper (see, e.g., damper 222 as shown in FIG. 1).

In other contemplated embodiments, the separate body of gas 626 in thesecond section 616 may be set to an initial pressure, such as by a pump(see, e.g., pump 230 as shown in FIG. 2), to bias the piston assembly618 to an initial position. The pressure of the second body of gas 626holds the piston assembly 618 in the initial position until the force ofgas supplied to the first section 614 via the inlet 624 exceeds theforce provided by the initial pressure of the separate body of gas 626in the second section 616.

The construction and arrangements of the gas spring assembly, as shownin the various exemplary embodiments, are illustrative only. Althoughonly a few embodiments have been described in detail in this disclosure,many modifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein. Someelements shown as integrally formed may be constructed of multiple partsor elements, the position of elements may be reversed or otherwisevaried, and the nature or number of discrete elements or positions maybe altered or varied. The order or sequence of any process, logicalalgorithm, or method steps may be varied or re-sequenced according toalternative embodiments. Other substitutions, modifications, changes andomissions may also be made in the design, operating conditions andarrangement of the various exemplary embodiments without departing fromthe scope of the present invention.

What is claimed is:
 1. A vehicle comprising: a body; a pair of frontwheel end assemblies; a pair of front gas springs coupling the frontwheel end assemblies to the body; a pair of rear wheel end assembliespositioned rearward of the front wheel end assemblies; and a pair ofrear gas springs coupling the rear wheel end assemblies to the body,wherein at least one of the rear gas springs comprises: a cylinder; arod extending within the cylinder and movable relative to the cylinder,the rod and the cylinder together at least partially defining a chamberhaving a variable volume and receiving a first pressurized gas therein;and an accumulator in communication with the chamber and containing asecond pressurized gas therein, the second pressurized gas within theaccumulator being held at a threshold pressure creating a first springrate opposing relative movement between the rod and the cylinder whenthe first pressurized gas within the chamber is pressurized below thethreshold pressure and a second spring rate opposing relative movementbetween the rod and the cylinder when the first pressurized gas withinthe chamber is pressurized above the threshold pressure.
 2. The vehicleof claim 1, wherein a pressure of the first pressurized gas is at leastpartially based upon a position of the rod relative to the cylinder. 3.The vehicle of claim 1, wherein the first spring rate is greater thanthe second spring rate.
 4. The vehicle of claim 1, wherein theaccumulator comprises a rigid exterior that defines an accumulatorvolume and a movable component internal to the rigid exterior.
 5. Thevehicle of claim 4, wherein the movable component separates theaccumulator volume into a first portion and a second portion, whereinthe first portion is in gaseous communication with the chamber and thethreshold pressure is a function of a pressure within the secondportion.
 6. The vehicle of claim 5, the accumulator further comprising aport in the rigid exterior configured to facilitate changing thepressure within the second portion.
 7. The vehicle of claim 6, whereinthe movable component comprises a diaphragm.
 8. The vehicle of claim 5,wherein the movable component is a bladder, the bladder containing thesecond pressurized gas therein.
 9. The vehicle of claim 1, furthercomprising a pair of dampers spaced apart from the rear gas springs andconfigured to oppose relative motion between the rear wheel endassemblies and the body.
 10. The vehicle of claim 1, wherein theaccumulator is a first accumulator, wherein at least one of the frontgas springs includes a second accumulator.
 11. A vehicle comprising: avehicle body; and a vehicle suspension system supporting the vehiclebody, the vehicle suspension system having a gas spring comprising: acylinder defining an inner chamber; a rod disposed within the cylinderand movable relative to the cylinder to adjust a volume of the innerchamber; and a sensor attached to at least one of the rod and thecylinder, wherein the sensor is configured to provide a signalindicative of a ride height of the vehicle suspension system based upona relative position of the rod and the cylinder.
 12. The vehicle ofclaim 11, wherein the sensor comprises a linear variable differentialtransformer.
 13. The vehicle of claim 12, wherein the sensor includes ashaft, and wherein the rod includes an end defining an aperture thatreceives the shaft of the sensor.
 14. The vehicle of claim 13, furthercomprising a tubular element having an inner space that receives theshaft of the sensor, the signal provided by the sensor relating to aninsertion length of the shaft into the tubular element.
 15. The vehicleof claim 11, wherein an inert gas is received within the inner chamber.16. A vehicle comprising: a body; a pair of front wheel end assemblies;a pair of front gas springs coupling the front wheel end assemblies tothe body; a pair of rear wheel end assemblies positioned rearward of thefront wheel end assemblies; and a pair of rear gas springs coupling therear wheel end assemblies to the body, wherein at least one of the reargas springs comprises: a rod movable relative to a cylinder, the rod andthe cylinder collectively defining a variable volume chambertherebetween; and an accumulator in gaseous communication with thevariable volume chamber, wherein the variable volume chamber receives afirst gas and the accumulator receives a second gas fluidly separatefrom the first gas, the second gas being pressurized to a thresholdpressure, and wherein the first gas provides different spring rates whenthe first gas is above or below the threshold pressure.
 17. The vehicleof claim 16, wherein the different spring rates include a first springrate and a second spring rate, the first spring rate corresponding towhen the first gas has a pressure below the threshold pressure and thesecond spring rate corresponding to when the first gas has a pressureabove the threshold pressure.
 18. The vehicle of claim 16, wherein asensor is disposed within at least one of the cylinder and the rod, andwherein the sensor is configured to provide a signal indicative of aride height of the vehicle based upon a relative position of the rod andthe cylinder.
 19. The vehicle of claim 18, wherein the sensor comprisesa linear variable differential transformer that includes a shaftextending through the cylinder to the rod.
 20. The vehicle of claim 16,further comprising a pump in communication with the accumulator, thepump being configured to compress the second gas.